1. Field of the Invention
The present invention relates to a dental composition, preferably a paste type dental composition, and more particularly to a dental composition, preferably a paste type dental composition which is mixable and is also capable of freely reproducing a color tone, and a set thereof. The dental composition is used for all kinds of dental materials (for example, fillers, temporary crowns, dental prostheses, implant upper structures, facing crowns and the like) produced from various materials (for example, composite materials, resins, ceramics and the like) which can be used in the dental field. The dental composition can also be directly applied to natural teeth.
2. Description of the Related Art
In current dental treatments, esthetic qualities are one of the most important elements and a dental material is strongly required to have properties so that a prosthesis has a color tone which resembles that of a natural tooth, and also has a beautiful white color.
In order to satisfy aesthetic elements in dental treatments, a dental crown color is reproduced by certain methods using ceramics and resin materials instead of metals. Of these materials, there have been remarkable developments in resin materials and materials having satisfactory abrasion resistance, bending strength, water resistance and the like have recently been proposed. A color sample (shade guide) is usually used with these ceramics and resin materials so as to match the color tone with that of a natural tooth and, therefore, a preliminarily colored material is provided in order to reproduce the color tone of the shade guide.
However, the natural tooth does not always have a single color tone and the color tone varies with a specific site. For example, the teeth of persons who smoke show color tones such as greenish brown color, reddish brown color, yellowish brown color and the like due to nicotine coloration, while a reddish purple or bluish purple pattern may appear on teeth influenced by tetracycline-based drugs. Also, overall color unevenness may be caused by disequilibrium of dental growth processes. In such a case, there is a limitation on the color tone reproduction only using a shade guide and a resin material having a basic color tone.
For the purpose of expressing higher esthetic qualities and the same color tone as that of a natural tooth, a material for partial coloration (stain material) has been proposed as a material having a color tone which is not possessed by the shade guide. The stain material generally is adjusted to various color tones such as brown color and purple color in order to reproduce a partial coloration of the tooth described above, and is also in the form of a liquid or a paste having a low viscosity so as to facilitate partial application to a prosthesis. Some stain materials have pure color tones such as red color, blue color, orange color and the like and are mainly used in combination with other color tones rather than used alone.
Surgical operators such as dentists, dental technicians and the like perform adjustment of the color tone of a dental crown prosthesis using a stain material having a color tone which has been adjusted preliminarily. When a color other than the color tone which has been adjusted preliminarily by a manufacturer is required, plural color tones are mixed. However, the stain material having a preliminarily adjusted color tone contains plural coloring materials (pigments, dyes) which have already been blended, and a more complicated color development structure is imparted by mixing these materials, and thus it is difficult to obtain the color tone desired by the surgical operator. In stain materials having pure colors such as red color, blue color, and orange color of conventional products, there was a limitation on the desired color mixture of the surgical operators in view of chromatology and subtractive color mixture.
Referring to a theory of color, the so-called three primary colors are classified into two kinds, which are the three additive primary colors and the three subtractive primary colors. In the case of the color tone of light, additive primary colors due to three colors of red, blue and green colors are established. The color tones using pigments or dyes such as those used in printing techniques are subtractive primary colors due to three colors of cyan, magenta and yellow colors.
It is theoretically possible to express all color tones by mixing the three subtractive primary colors of cyan, magenta and yellow colors in any concentration on a white-colored base. However, in current printing techniques, complete black may not be obtained even by mixing existing colored materials of cyan, magenta and yellow colors, in many cases. Therefore, in addition to the three subtractive primary colors, a black coloring material is used practically and is generally called CMYK (Cyan, Magenta, Yellow, Key plate). In case coloration on a white-colored base cannot be performed when the color tone is expressed by three subtractive primary colors, it becomes necessary to further use a white colored coloring material.
As a color expressing method, an expression method using a color sample provided by a manufacturer has mainly been used over a long time in the dental field. However, a L*a*b* color system, which is often used in the industrial field, has recently been used in combination. However it has been suggested that complete agreement with human sense of color is not achieved by the L*a*b* color system. A theory advocating the utility of a Munsell color system is disclosed in “Color for Dentistry, Method for Expression of Dental Crown using Munsell Color System” (written by Ikuemon Katayama, published by Japan Academy of Color for Dentistry, 2005, December, Vol. 11, No. 1, P. 39-44). This document describes that evaluation by the Munsell color system agrees with a human evaluation with respect to a dental crown material.
Here, a color expression system as a method of expressing a color tone will be described. Also in the present invention, the invention is explained using two kinds of color systems. First, a L*a*b* color system is defined by CIE (Commission internationale de l'éclairage) and a color is expressed by a lightness index L* and a perceptive chromaticity index a* and b*. This L*a*b* color system is widely used as a uniform perceptual color space in the industrial field. In contrast, a Munsell color system is an expression method by a sensation when a color chip is visually observed, a so-called perceived color. The color is expressed by systematically classifying various colors and defining a scale graduation with respect to each attribute of a color value (symbol V), chromaticness (symbol C) and hue (symbol H). Specifically, the value of color (V) is expressed by the numerical value of 0 to 10 and with respect to the chromaticness, different scale graduation is defined every hue. The hue is expressed by arranging 10 hues of basic hue, red (R), yellow (Y), green (G), blue (B), purple (P), and complementary colors of these basic hues, such as bluish green (BG), bluish purple (BP), reddish purple (RP), yellowish red (YR) and yellowish green (GY) on a 360 degree circumference.
As described above, recent demands for color tone expression have rapidly increased in the dental field, and it has become necessary to develop a dental material which responds to such demand.
JP-A No. 2004-203865 discloses a dental coating material comprising (A) a matrix resin, (B) a filler mixture, (C) one or more kinds of polymerization initiators, and (D) a trace amount of one or more kinds of dental pigments. The invention relates to a coating material which can be used by a brush and is used to adjust a color tone of an artificial tooth.
JP-A No. 2005-112854 discloses a method for correcting a color of a surface of dental prostheses or teeth by applying a photocurable correcting color for a dental basic color. The invention relates to the technique in which correcting colors of orange, blue, white and black colors are used so as to adjust a basic color which is widely used in the dental field. However, application to a peculiar color tone of a specific site of teeth is not possible and definition of the correcting color is chromatologically unclear. Thus it is considered to be impossible to cope with various color tones required for the dental prostheses.
“The Journal of the Japan Dental Technicians' Association, New Placement Technique of Photopolymerizable Rigid Resin” (written by Yasuo Onodera, published by The Japan Dental Technicians' Association (Incorporated), issued on 2006, November, Page. 33-40) describes reproduction of a color of a tooth using an internal stain. However, the method is a method in accordance with the shade guide and had a problem that it is impossible to perform entire color tone reproduction.